The invention relates to a flotation system for a header of an agricultural machine and although it will be discussed primarily in relation to combine harvesters, it is to be understood that it is applicable to any other type of agricultural machine which employs a header, such as a forage harvester, for example.
Combine harvesters, particularly the self-propelled type, are equipped to utilise a variety of crop-gathering headers, including headers specifically designed for harvesting corn, cereal grains or soy beans, for example. Normally, these headers are attached to the forward end of a feeder housing which is a structure used to convey crop material from the header to a base unit of the combine harvester for further harvesting treatment. As is shown in U.S. Pat. No. Re. 26,512, the forward end of the feeder housing can be constructed so that the header can be quickly and easily attached thereto. Usually, the feeder housing structure is rectangular in cross section and includes a rectangular crop inlet opening at the forward end which matches with a crop outlet opening of a header attached to the feeder housing.
With the modern trend of developing headers of increasingly larger sizes, providing a ready capability for the headers to follow the contours of the ground is vital. One type of prior art leveling or flotation mechanism, such as disclosed in U.S. Pat. No. 3,981,125, involves the twisting of the feeder housing structure about the generally fore-and-aft extending centerline thereof to effect an associated lateral floating movement of the header. Also hillside combine harvesters have been developed to allow the header to follow slopes of up to 45%. Such hillside combine harvesters have been known to utilise a side pivot mechanism, as disclosed in U.S. Pat. No. 3,731,470, or a center-mounted pivot connection directly between the header and the feeder housing as disclosed in U.S. Pat. No. 2,780,903; the latter arrangement involving a specific circular or semi-circular opening between the feeder housing and the header.
Problems that have been encountered with these prior art lateral float mechanisms include a difficult sealing situation between the feeder housing and the base unit as the feeder housing is twisted relative to the base unit. The twisting of the feeder housing also results in a twisting of the feeder housing drive mechanism, which in turn also increases wear and reduces the life of the drive chains or the like. Another problem encountered is the matching of different types of headers to different feeder housing structures. This problem is particularly relevant to feeder housings having specially shaped crop inlet openings.
In other known header flotation systems use is made of one or two hydraulic actuators connected between the header and the base unit of a machine to pivot the header in a transverse direction around a generaly fore-and-aft pivot axis and which are interconnected hydraulically with a header weight compensation device including control actuators together with a hydro-pneumatic accumulator which effect raising and lowering of the header. In operation, the hydraulic system, inclusive the hydro-pneumatic accumulator is pressurized at a operating pressure such that the ground contact pressure of the header is minimal. This allows the header to follow the irregularities in the ground contour by as well raising or lowering the complete header as by pivoting the header in the transverse direction depending on the size of the irregularities and on the location thereof relative to the header. With headers having a weight imbalance, such as grain headers having the drive means located at one side, a single flotation actuator can be used at the side of the drive means, but with balanced headers, two flotation actuators are used, one at or towards each side of the header.
In still another known header flotation system such as disclosed in U.S. Pat. No. 3,386,235, the header is formed in two parts which can pivot independently from each other and relative to the feeder housing around respective fore-and-aft extending pivot axes. These parts also can be raised or lowered in unison together with the feeder housing upon which they are mounted, around a transverse pivot axis. A hydraulic suspension system, including cylinders supporting the feeder housing with the header thereon on the base unit and further cylinders supporting the header portions on the feeder housing, is coupled to a hydraulic control mechanism which is actuated by variations in hydraulic pressure in the respective cylinders in response to corresponding movements of the header, respectively the constituent portions thereof over undulations in the ground. The arrangement is such that said variations in pressure transmitted to the control mechanism cause the control mechanism to allow hydraulic pressure fluid to flow to or from the respective cylinders so as to compensate for said variations and tend to maintain a substantially constant hydraulic pressure in the respective cylinders. Hydro-pneumatic accumulators, operating at the system pressure, are coupled to the various cylinders for assisting in a smooth following of the ground irregularities by the header and the constituent portions thereof.
With the latter two systems, the header must always be in contact with the ground at least at some point along its length so that these headers cannot be set to operate at a given stubble height, for example, which is a disadvantage. This is not so with an automatic header height and lateral flotation control system such as disclosed in the co-pending European patent application No. 86.200.600 and which uses sensors on the underside of the header. Such sensors produce electrical signals for controlling the flotation actuators via electro-hydraulic valves, thus making the system automatic. However, other disadvantages arise with such automatic systems, the main one of which is that they are slow acting. Furthermore, these systems are expensive and the sensors thereof can suffer damage when the header encounters a large obstruction and the header tilting is too slow to clear this obstruction smoothly. The slow-acting nature of such automatic systems also can place excessive torsional forces on the header and front end of the machine to which it is fitted (for example the feeder housing of a combine harvester) when the header tilts on meeting an irregularity in the ground and until the system has responded and effected the required flotation to compensate. Although an automatic system can operate with the header off the ground because it is not part of a header weight compensation system, it cannot be set to give any desired initial position of the header which deviates from the nominal position of the header because the electrohydraulic control valves for the flotation actuators can only be set through the sensors.